MPLS Working Group Z. Ali
G. Swallow
Internet Draft Cisco Systems, Inc.
R. Aggarwal
Juniper Networks
Intended status: Standard Track August 17, 2011
Expires: February 16, 2012
Non Penultimate Hop Popping Behavior and out-of-band mapping forRSVP-TE Label Switched Pathsdraft-ietf-mpls-rsvp-te-no-php-oob-mapping-09.txt
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Abstract
There are many deployment scenarios which require Egress Label
Switching Router (LSR) to receive binding of the Resource
ReserVation Protocol Traffic Engineered (RSVP-TE) Label Switched
Path (LSP) to an application, and payload identification, using
some "out-of-band" (OOB) mechanism. This document defines
protocol mechanisms to address this requirement. The procedures
described in this document are equally applicable for point-to-
point (P2P) and point-to-multipoint (P2MP) LSPs.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
RFC 2119 [RFC2119].
Table of Contents
Copyright Notice ..............................................11. Introduction ...............................................32. RSVP-TE signaling extensions ...............................42.1. Signaling non-PHP behavior ............................42.2. Signaling OOB Mapping Indication ......................52.3. Relationship between OOB and non-PHP flags ............72.4. Egress Procedure for label binding ....................73. Security Considerations ....................................84. IANA Considerations ........................................84.1. Attribute Flags for LSP_ATTRIBUTES object .............84.2. New RSVP error sub-code ...............................9 Expires February 2012 [Page 2]

Internet-Draft draft-ietf-mpls-rsvp-te-no-php-oob-mapping-09.txt5. Acknowledgments ............................................96. References .................................................96.1. Normative References ..................................96.2. Informative References ...............................101. Introduction
When Resource ReserVation Protocol Traffic Engineered (RSVP-TE)
is used for applications like Multicast Virtual Private Network
(MVPN) [MVPN] and Virtual Private LAN Service (VPLS) [RFC4761],
an Egress Label Switching Router (LSR) receives the binding of
the RSVP-TE Label Switched Path (LSP) to an application, and
payload identification, using an "out-of-band" (OOB) mechanism
(e.g., using Border Gateway Protocol (BGP)). In such cases, the
Egress LSR cannot make correct forwarding decision until such OOB
mapping information is received. Furthermore, in order to apply
the binding information, the Egress LSR needs to identify the
incoming LSP on which traffic is coming. Therefore, non
Penultimate Hop Popping (non-PHP) behavior is required to apply
OOB mapping. Non-PHP behavior requires the egress LSRs to assign
a non-NULL label for the LSP being signaled.
There are other applications that require non-PHP behavior. When
RSVP-TE point-to-multipoint (P2MP) LSPs are used to carry IP
multicast traffic non-PHP behavior enables a leaf LSR to identify
the P2MP TE LSP, on which traffic is received. Hence the egress
LSR can determine whether traffic is received on the expected P2MP
LSP and discard traffic that is not received on the expected P2MP
LSP. Non-PHP behavior is also required to determine the context of
upstream assigned labels when the context is a MPLS LSP. Non-PHP
behavior may also be required for MPLS-TP LSPs [RFC5921].
This document defines two new flags in the Attributes Flags TLV
of the LSP_ATTRIBUTES object defined in [RFC5420]: one flag for
communication of non-PHP behavior, and one flag to indicate that
the binding of the LSP to an application and payload identifier
(payload-Id) needs to be learned via an out-of-band mapping
mechanism. As there is one-to-one correspondence between bits in
the Attribute Flags TLV and the RRO Attributes subobject,
corresponding flags to be carried in RRO Attributes subobject are
also defined.
The procedures described in this document are equally applicable
for P2P and P2MP LSPs. Specification of the OOB communication
mechanism(s) is beyond the scope of this document.
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Internet-Draft draft-ietf-mpls-rsvp-te-no-php-oob-mapping-09.txt2. RSVP-TE signaling extensions
This section describes the signaling extensions required to
address the above-mentioned requirements.
2.1. Signaling non-PHP behavior
In order to request non-PHP behavior for an RSVP-TE LSP, this
document defines a new flag in the Attributes Flags TLV of the
LSP_ATTRIBUTES object defined in [RFC5420]:
Bit Number (to be assigned by IANA): non-PHP behavior requested flag.
In order to indicate to the Ingress LSR that the Egress LSR
recognizes the "non-PHP behavior requested flag", the following
new bit is defined in the Flags field of the Record Route object
(RRO) Attributes subobject:
Bit Number (same as bit number assigned for non-PHP behavior
requested flag): Non-PHP behavior acknowledgement flag.
An Ingress LSR sets the "non-PHP behavior requested flag" to
signal the egress LSRs SHOULD assign non-NULL label for the LSP
being signaled. This flag MUST NOT be modified by any other LSRs
in the network. LSRs other than the Egress LSRs SHOULD ignore
this flag.
If an egress LSR receiving the Path message, supports the
LSP_ATTRIBUTES object and the Attributes Flags TLV, and also
recognizes the "non-PHP behavior requested flag", it MUST
allocate a non-NULL local label. The egress LSR MUST also set the
"Non-PHP behavior acknowledgement flag" in the Flags field of the
RRO Attribute subobject.
If the egress LSR
- supports the LSP_ATTRIBUTES object but does not recognize the
Attributes Flags TLV; or
- supports the LSP_ATTRIBUTES object and recognize the Attributes
Flags TLV, but does not recognize the "non-PHP behavior requested
flag";
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then it silently ignores this request according to the processing
rules of [RFC5420].
An ingress LSR requesting non-PHP behavior SHOULD examine "Non-
PHP behavior acknowledgement flag" in the Flags field of the RRO
Attribute subobject and MAY send a Path Tear to the Egress which
has not set the "Non-PHP behavior acknowledgement flag". An
ingress LSR requesting non-PHP behavior MAY also examine the
label value corresponding to the Egress LSR(s) in the RRO, and
MAY send a Path Tear to the Egress which assigns a Null label
value.
When signaling a P2MP LSP, a source node may wish to solicit
individual response to the "non-PHP behavior requested flag" from
the leaf nodes. Given the constraints on how the LSP_ATTRIBUTES may
be carried in Path and Resv Messages according to RFC5420, in
this situation the source node MUST use a separate Path message for
each leaf in networks where [ATTRIBUTE-BNF] is not supported. In
networks with [ATTRIBUTE-BNF] deployed either separate Path
message for each leaf or multiple leafs per Path message MAY be
used by the source node.
2.2. Signaling OOB Mapping Indication
This document defines a single flag to indicate that the normal
binding mechanism of an RSVP session is overridden. The actual
out-of-band mappings are beyond the scope of this document. The
flag is carried in the Attributes Flags TLV of the LSP_ATTRIBUTES
object defined in [RFC5420] and is defined as follows:
Bit Number (to be assigned by IANA): OOB mapping indication flag.
In order to indicate to the Ingress LSR that the Egress LSR
recognizes the "OOB mapping indication flag", the following new
bit is defined in the Flags field of the Record Route object
(RRO) Attributes subobject:
Bit Number (same as bit number assigned for OOB mapping
indication flag): OOB mapping acknowledgement flag.
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An Ingress LSR sets the OOB mapping indication flag to signal the
Egress LSR that binding of RSVP-TE LSP to an application and
payload identification is being signaled out-of-band. This flag
MUST NOT be modified by any other LSRs in the network. LSRs
other than the Egress LSRs SHOULD ignore this flag.
When an Egress LSR which supports the "OOB mapping indication
flag", receives a Path message with that flag set, the Egress LSR
MUST set the "OOB mapping acknowledgement flag" in the Flags
field of the RRO Attribute subobject. The rest of the RSVP
signaling proceeds as normal. However, the LSR MUST have
received the OOB mapping before accepting traffic on the LSP.
This implies that the Egress LSR MUST NOT setup forwarding state
for the LSP before it receives the OOB mapping.
Note that the payload information SHOULD be supplied by the OOB
mapping. If the egress LSR receives the payload information from
OOB mapping then the LSR MUST ignore L3PID in the Label Request
Object [RFC3209].
If the egress LSR
- supports the LSP_ATTRIBUTES object but does not recognize the
Attributes Flags TLV; or
- supports the LSP_ATTRIBUTES object and recognizes the
Attributes Flags TLV, but does not recognize the "OOB mapping
indication flag";
then it silently ignores this request according to the processing
rules of [RFC5420].
An ingress LSR requesting OOB mapping SHOULD examine "OOB mapping
acknowledgement flag" in the Flags field of the RRO Attribute
subobject and MAY send a Path Tear to the Egress which has not
set the "OOB mapping acknowledgement flag".
When signaling a P2MP LSP, a source node may wish to solicit
individual response to the "OOB mapping indication flag" from the
the leaf nodes. Given the constraints on how the LSP_ATTRIBUTES
may be carried in Path and Resv Messages according to RFC5420, in
this situation the source node MUST use a separate Path message for
each leaf in networks where [ATTRIBUTE-BNF] is not supported. In
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networks with [ATTRIBUTE-BNF] deployed either separate Path
message for each leaf or multiple leafs per Path message MAY be
used by the source node.
In deploying applications where Egress LSR receives the binding
of the RSVP-TE LSP to an application, and payload identification,
using OOB mechanism, it is important to recognize that the OOB
mapping is sent asynchronously with respect to the signaling of
RSVP-TE LSP. Egress LSR only installs forwarding state for the LSP
after it receives the OOB mapping. In deploying applications using
OOB mechanism, an Ingress LSR may need to know when the Egress is
properly setup for forwarding (i.e., has received the OOB mapping).
How the Ingress LSR determines that the LSR is properly setup for
forwarding at the Egress LSR is beyond the scope of this document.
Nonetheless, if the OOB mapping is not received by the Egress LSR
within a reasonable time, the procedure defined in section 2.4 to
tear down the LSP is followed.
2.3. Relationship between OOB and non-PHP flags
"Non-PHP behavior desired" and "OOB mapping indication" flags can
appear and be processed independently of each other. However, as
mentioned earlier, in the context of the applications discussed in
this document, OOB mapping requires non-PHP behavior. An Ingress
LSR requesting the OOB mapping MAY also set the "non-PHP behavior
requested flag" in the LSP_ATTRIBUTES object in the Path message.
2.4. Egress Procedure for label binding
RSVP-TE signaling completion and the OOB mapping information
reception happen asynchronously at the Egress. As mentioned in
Section 2.2, Egress waits for the OOB mapping before accepting
traffic on the LSP. Nonetheless, MPLS OAM mechanisms, e.g., LSP
Ping and Trace route as defined in [RFC4379], [P2MP-OAM], are
expected to work independent of OOB mapping learning process.
In order to avoid unnecessary use of the resources and possible
black-holing of traffic, an Egress LSR MAY send a Path Error
message if the OOB mapping information is not received within a
reasonable time. This Path Error message SHOULD include the error
code/sub-code "Notify Error/ no OOB mapping received" for all
affected LSPs. If notify request was included when the LSP was
initially setup, Notify message (as defined in [RFC3473]) MAY
also be used for delivery of this information to the Ingress LSR.
An Egress LSR MAY implement a cleanup timer for this purpose. The
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time-out value is a local decision at the Egress, with a
RECOMMENDED default value of 60 seconds.
3. Security Considerations
Addition of "non-PHP behavior" adds a variable of attacks on the
label assigned by the Egress node. As change in the value of the
egress label reported in the RRO can cause the LSP to be torn
down, additional security considerations for protecting label
assigned by the Egress node are required. Security mechanisms as
identified in [RFC5920], [RFC2205], [RFC3209], [RFC3473],
[RFC5420] and [RFC4875] can be used for this purpose. This
document does not introduce any additional security issues above
those identified in [RFC5920], [RFC2205], [RFC3209], [RFC3473],
[RFC5420] and [RFC4875].
4. IANA Considerations
The following changes to the Resource Reservation Protocol-Traffic
Engineering (RSVP-TE) Parameters registry are required.
4.1. Attribute Flags for LSP_ATTRIBUTES object
The following new flags are defined for the Attributes Flags TLV
in the LSP_ATTRIBUTES object. The numeric values are to be
assigned by IANA.
o Non-PHP behavior flag:
This flags is used in the Attributes Flags TLV in a Path message.
The flags have corresponding new flag to be used in the RRO
Attributes subobject. As per [RFC5420], the bit numbering in the
Attribute Flags TLV and the RRO Attributes subobject is
identical. That is, the same attribute is indicated by the same
bit in both places. This flag is not allowed in the Attributes
Flags TLV in a Resv message. Specifically, Attributes of this
flag are as follows:
- Bit Number: To be assigned by IANA.
- Attribute flag carried in Path message: Yes
- Attribute flag carried in Resv message: No
- Attribute flag carried in RRO message: Yes
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o OOB mapping flag:
This flags is used in the Attributes Flags TLV in a Path message.
The flags have corresponding new flag to be used in the RRO
Attributes subobject. As per [RFC5420], the bit numbering in the
Attribute Flags TLV and the RRO Attributes subobject is
identical. That is, the same attribute is indicated by the same
bit in both places. This flag is not allowed in the Attributes
Flags TLV in a Resv message. Specifically, Attributes of this
flag are as follows:
- Bit Number: To be assigned by IANA.
- Attribute flag carried in Path message: Yes
- Attribute flag carried in Resv message: No
- Attribute flag carried in RRO message: Yes
4.2. New RSVP error sub-code
For Error Code = 25 "Notify Error" (see [RFC3209]) the following
sub-code is defined.
Sub-code Value
-------- -----
No OOB mapping received to be assigned by IANA.
5. Acknowledgments
The authors would like to thank Yakov Rekhter for his suggestions
on the draft.
6. References6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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